The Neurobiology Core will provide several Animal Models of neuronal plasticity in rats to each project. The Director has extensive experience with dealing with intracerebral microinjections into rats and will adhere closely to NIH Animal Welfare guideline. It has been demonstrated that selective removal of serotonergic fibers from the hippocampus by microinjections through a glass pipettes produces minimal damage to non- serotonergic fibers passing through the same pathways. The use of the glass pipette ensure that the entire volume can be uniformly injected over a prolonged period of time. This slow delivery, coupled with angled electrode placements is designed to minimize the non-specific damage to the brain neuropil. In addition, the superior and inferior longitudinal sinus and the ventricular system are avoided where possible. The animal models we propose to supply will include selective-chemical degeneration of 5-HT fiber in hippocampus, DA fibers in caudate, and Ach cells in the medial nucleus. Acute response of the fibers to injury and chronic regenerative sprouting will be assessed. In addition, fetal neuronal (5-HT, DA or Ach) transplantation into hippocampus, cortex or caudate will be available to measure fetal neurite outgrowth and long-term interactions with host brain. These animals will injected with drugs or factors as indicated. Intracerebral injections of radioactive compounds, antibodies or experimental cells will be made into selected brain sites. Neuronal plasticity will be measured by reuptake assays, HPLC and immunocytochemistry. A senior technician experienced in all aspects of the neurosurgery will perform all surgery. A certified veterinarian supervises post-operative care in the animals receiving any type of surgery. The director will consult with the respective project PIs to protocol all studies before execution of the experiments. Special attention will be given to provide all the necessary control groups, perform all crucial morphometric procedures with coded slides, and apply adequate statistical analysis of the raw data. Photographs of morphological changes and results (raw data and statistical analysis) will be sent to the project PIs. The original material will be organized and stored at New York University.